Hybrid AC-DC Microgrid Research Articles

Coordination Control and Energy Management of Standalone Hybrid AC/DC Microgrid

An efficient energy management scheme for a standalone hybrid AC/DC microgrid (HMG) has been proposed in this paper. Energy management in a microgrid is a challenging task, because of the involvement of the distributed energy resources (DERs) which are intermittent in nature. The microgrid may therefore, undergo mismatch in demand and supply, when either the generation or load varies. This mismatch in power may result into DC bus voltage deviations and sometimes these deviations may be out of the permissible limits. A coordination control-based strategy (CCS) for DC bus voltage deviation mitigation and efficient energy management of the standalone microgrid is investigated here. The CCS is tested with the help of simulation studies on a test hybrid AC/DC microgrid in MATLAB covering all the scenarios which may arise. The test microgrid consists of a solar photovoltaic (PV) generation, a secondary source of generation, PEM fuel cell, a battery and a super capacitor. Coordination between the various sub-units and energy management of hybrid AC/DC microgrid is done using Fuzzy Logic Control (FLC) and the DC bus voltage deviations are also compared with PI based control system. It is found that the system with FLC has better performance than PI based control system.

Parallel AC-DC interlinking converters in the proposed grid-connected hybrid AC-DC microgrid; planning

The hybrid AC-DC microgrid was developed by connecting the AC, and DC microgrids through a bi-directional AC-DC interlinking converter. The proposed hybrid AC-DC microgrid is created by adding a series converter between the DC bus and utility for compensation of utility voltage power quality problems. The parallel interlinking converters could enhance the capacity of apparent power exchanging between the AC and DC buses, SIC. This paper investigates a tradeoff between two objectives including the annualized investment cost, and reliability index cost, for finding an optimum number (n) of parallel interlinking converters. The solving procedure is performed as a two-stage hierarchical problem. In the first stage, SIC is calculated by considering the power flow satisfaction and power quality improvement. The reliability analysis is done by extraction of the expected apparent power shortage index (EVAS). In the second stage, a decision-making process is adopted to select a proper solution (n) with minimization of the annualized investment cost, and reliability index cost. The simulations are executed on a typical grid-connected proposed hybrid AC-DC microgrid with experimental data of the AC and DC DGs and loads. Simulation results show the effectiveness of the proposed method for finding an optimum number of parallel interlinking converters.

Performance analysis of hybrid AC / DC microgrid under influence of battery energy storage location

In microgrids, energy storage is generally located based on power management criteria and economic objectives that lean on the system's steady-state operation. However, the grid configuration, dynamics of primary energy sources, and storage type (AC or DC) impact its transient operation. This paper conducts a comparative study of the dynamic performance of Hybrid AC/DC Microgrids (HMGs) under the influence of Battery Energy Storage System (BESS) location, which has been neglected in the literature. The HMG performance is compared for one single BESS unit located either in AC or DC sub-grid during various grid operational cases, considering interlinking converter (ILC) control topology that alters depending on the type of BESS. Two types of microgrid case studies with different structures have been considered, that is, a high inertia HMG and a converter-interfaced low inertia HMG. Simulation results reveal that the HMGs with both BESS locations perform robustly in handling grid disruptions. However, the BESS located in the DC sub-grid of a high inertia microgrid case presents an average of 40% higher quality of performance in key performance indicators compared to that of the AC sub-grid BESS. Conversely, the performance of the low inertia HMG with the BESS connected to the AC sub-grid is superior to that of the DC sub-grid BESS, by an average of 65% and 54% in key performance indicators.

Intelligent fuzzy-based controllers for voltage stability enhancement of AC-DC micro-grid with D-STATCOM

Voltage stability and power quality play very effective issues in power systems. This paper aims to improve the voltage stability and enhance system power quality in the AC-DC micro-grid system based on intelligent fuzzy controllers. These controllers are fuzzy-PI (FPI) and fuzzy-PID (FPID) current-controller with the existence of distribution static synchronous compensator (D-STATCOM). The capability of proposed system has been applied in two case studies that emulate abrupt fault and dynamic load changes on AC-DC hybrid micro-grid that collects different types of renewable energy sources. In addition to, the proposed fuzzy-based controllers produce the optimum dynamic response and resolve the power quality issues. Numerical simulations associated with detailed comparisons between different controllers are provided. It was found that when the studied system is subjected to a 3-phase fault, the voltage fluctuation at the D-STATCOM is reduced by 7.86% and 4.62% and the dynamic system performance is improved by 12.9% and 8.8% with using Fuzzy-PID and fuzzy-PI, respectively. Also with the dynamic load changes, the fluctuation of system voltages at the D-STATCOM is reduced by 0.982% and 0.577 % and the dynamic system performance is improved with 6.67%, 5.71% when comparing Fuzzy-PID controller and Fuzzy-PI to the uncontrolled system. The Fuzzy-PID provides a capability to enhance dynamic performance and system power quality because achieve less fluctuation and more smoothing for signals makes it is superior for voltage control for AC-DC micro-grid.

Interconnected hybrid AC-DC microgrids security enhancement using blockchain technology considering uncertainty

Recently, interconnected (networked) hybrid AC-DC microgrids have been attracted lots of attentions due to both technical and economic advantages, compared to the conventional interconnected microgrids. In such a system, the DC sources, e.g., solar energies, are connected to the DC busses, while the AC sources, e.g., wind turbines, are connected to the AC busses. Hence, the entire efficiency of the system can be increased significantly. Also, it is more economical than the conventional grids due to removing power electronics interfaces that convert DC to AC power. Although there exist many advantages associated with such a system, there exist many challenges as well. For instance, the energy management of the system, from the system level perspective is more challenging since any changes in any subsystem (AC or DC parts) can potentially affect the energy management of the entire system. To this end, in this paper, a new modified sine cosine algorithm (SCA) is developed to find the optimal solution. Moreover, to increase the security of the power trading within the hybrid AC-DC networked microgrids, the blockchain technology is used and adopted. To make a realistic model, a stochastic load flow, based on copula mode has also been employed. Results demonstrate the effectiveness of the proposed blockchain-based hybrid networked AC-DC microgrid energy management framework.

Performance Enhancement of a Hybrid AC-DC Microgrid Operating with Alternative Energy Sources Using Supercapacitor

Microgrids with non-conventional energy sources have become popular recently. Hybrid AC-DC microgrid (HMG) architecture is effectual as it avoids several power conversions for the consumers. Therefore, this article presents a comprehensive study on grid-tied HMG with PV array and wind energy conversion system (WECS) as principal sources. Fuel cell (FC) acts as the auxiliary source in the DC subgrid and the supercapacitor (SC) is used for instantaneous energy management. The hydrogen storage system is used to store surplus power produced by the PV array. The power flow between the subgrids is regulated using the interlinking converter (ILC) by a PQ controller. The main contribution of this article is the comparative investigation of system operation in the HMG configuration in the presence and absence of a supercapacitor bank on the DC bus. The maximum DC bus voltage fluctuation during load variations in the absence and presence of SC bank is found to be 6.6 V and 3.9 V respectively. Similarly, the maximum transient fluctuation in the power supplied to the DC load is found to be 830 W in the absence of SC bank and 340 W in the presence of SC bank

A Bus-Sectionalized Hybrid AC/DC Microgrid: Concept, Control Paradigm, and Implementation

In the last several years, the coordination control of hybrid AC/DC microgrids (HMGs) has been gaining increasingly more attention. However, most of these discussions are focused on single-bus HMGs whose AC or DC bus is not sectionalized by AC or DC breakers. Compared with these single-bus HMGs, the bus-sectionalized HMG has more flexible topologies, more diverse operation modes, and consequently higher service reliability. However, meanwhile, these benefits also bring challenges to the stable operation of bus-sectionalized HMGs, particularly for mode switching. Relying on the national HMG demonstrative project in Shaoxing, China, this paper makes efforts to present the hierarchical control paradigm of a typical bus-sectionalized HMG toward standardization. The test results demonstrate that the proposed system provides seamless switching and uninterrupted power supply without controller reconfiguration among different operation modes. The operational data are also brought forth and analyzed to provide significant and useful experiences for designing and developing similar HMGs in the future.

A Novel AC-DC Hybrid Microgrid Control Strategy Based on VSM

It is an important goal of the microgrid control system to realize the rational allocation of power between the AC and DC microgrid by using the power electronic converter to integrate the renewable energy into the power distribution system. This paper introduces the Virtual Synchronous Generator (VSM) control strategy of hybrid microgrid, which solves the above problems by mimicking the characteristics of traditional Synchronous Machine (SM). In order to better optimize the performance of AC/DC hybrid microgrid, a novel VSM-based bidirectional converter (BC) control strategy is proposed, which also ensures the capability of BC independent power allocation. Finally, in the PSCAD environment, two types are used. The hybrid microgrid with different BC control structures was studied and compared.

A Benefit Evaluation Model for Peak-Clipping Benefits of Distributed Photovoltaic Grids Taking into Account Uncertain Low-Voltage Distribution

Due to the high energy consumption in the traditional AC-DC hybrid microgrid, the benefit evaluation may be difficult. In this paper, an AC-DC low-voltage hybrid distribution network suitable for distributed photovoltaic power generation access is proposed. DC power directly supplies DC household appliances, and AC power grid directly supplies AC appliances. In this way, the loss of electric energy in the process of energy conversion can be reduced, and good economy can be achieved. The 24-pulse thyristor bidirectional converter is used in the connection between AC and DC power grids, which can reduce the loss and prevent the failure of benefit evaluation. The photovoltaic low-voltage distribution tracking adopts conductance increment method, and the converter control adopts constant voltage control to maintain the bus voltage stability. The simulation results prove the feasibility of the scheme.

Stochastic energy management and scheduling of microgrids in correlated environment: A deep learning-oriented approach

Regarding the operation, reliability, security, and cost-effectiveness of microgrids (MGs), optimal energy management and data security are essential issues that must be taken into consideration. In this regard, this paper proposes a secured stochastic energy management scheme for both grid-connected and islanded hybrid AC-DC MGs (HMGs) considering renewable energy sources (RESs), plug-in hybrid electric vehicles (PHEVs), and energy storage devices (ESs). In this work, the operation of HMGs is formulated as a single objective optimization problem, which is solved using the interior search optimization algorithm (ISOA). In order to reinforce data security in HMGs, a deep learning-based intrusion detection system (IDS) based on the long short-term memory (LSTM) and prediction interval is proposed to detect false data injection attacks (FDIA) on advanced metering infrastructures (AMIs). In this work, the 2 m point estimation method is utilized to model uncertainties associated with the forecasted output power of RESs, energy market price, charging demand of PHEVs, and load demand. The performance of the proposed scheme is evaluated using IEEE 33 bus test system for both operation modes.

Control method for improvement of power quality in single interlinking converter hybrid AC‐DC microgrids

Hybrid AC-DC microgrids (HMGs) are formed by interconnecting AC microgrids (MGs) and DC microgrids via AC-DC interlinking converters (ICs). In the islanded mode, apart from power sharing in a single MG, power sharing expansion throughout HMG is desirable. Conventionally, this is achieved by employing an IC control mechanism in coordination with the droop characteristics of sources. Because the conventional control strategy of IC relies on measuring the frequency variations in AC MG, accurate coordination necessitates a wide range of frequency deviation. Also, this strategy employs the current-controlled method, which fails to accomplish superior voltage quality during load transients and in the presence of an unbalanced load obtainable by the voltage-controlled method (VCM). An IC control strategy for single IC HMGs is proposed that does not require the measurement of frequency variation and employs VCM in the inner control loop. As a consequence, the power quality of AC MG is improved. The proposed control strategy is phase locked-loop-less. In addition, by supporting the related MG with the disconnection of sources in AC MG or DC MG, it provides a uniform control property. Time domain simulations and experimental results are provided to verify the efficacy of the proposed strategy.

Hybrid machine learning based energy policy and management in the renewable-based microgrids considering hybrid electric vehicle charging demand

In this paper, a secured energy management architecture for both islanded and grid-connected operation modes of renewable hybrid AC-DC microgrids considering various renewable energy sources, distributed power generation units, energy storage, and plug-in hybrid electric vehicles (PHEV) is proposed. In this architecture, whale optimization algorithm (WOA) is employed to minimize the operation cost of the grid and also an intrusion detection system (IDS) based on the sequential hypothesis testing (SHT) approach is introduced to detect identity-based cyber-attacks (i.e. Sybil attack, masquerading attack) on the wireless-based advanced metering infrastructures (AMI). The proposed IDS makes use of the received signal strength (RSS) value to distinguish different signal sources and detect cyber-attacks. The feasibility and performance of the proposed architecture are tested on a practical hybrid microgrid, which is constructed based on the IEEE 33-bus test system. the results are provided for both islanded and grid-connected operation modes.

Distributed Control in Hybrid AC-DC Microgrids Based on a Hybrid MCSA-ADMM Algorithm

This paper proposes an effective framework for optimal operation management of hybrid AC-DC microgrids incorporating both dispatchable and non-dispatchable energy sources as well as battery storage. The proposed method is constructed based on a fully distributed consensus-based structure making use of a multi-agent mechanism and alternating direction method of multipliers (ADMM). The proposed framework decomposes the microgrid into several agents within which the neighboring agents share the consensus variable (mismatch power flow) with each other. Each agent tries to minimize its own cost based on the consensus variable value received from the other agents. An augmented objective function is then formulated which is nonlinear and needs to be optimized. Due to the high nonlinearity of the objective function, a new optimization method based on crow search algorithm (CSA) is developed to find the optimal local solutions for each agent and drive the ADMM to have a mature convergence. A modified method based on crossover and mutation operators is introduced to increase the search ability of CSA. The performance of the proposed framework is assessed using a typical hybrid AC-DC microgrid with distributed energy resources. The simulation results show the high efficacy of the proposed method in comparison with other methods.

Novel Power Smoothing Technique for a Hybrid AC-DC Microgrid Operating with Multiple Alternative Energy Sources

The power produced by renewable sources such as photovoltaic systems and wind energy conversion systems is highly intermittent due to continuously changing irradiance and wind velocity. When the distributed generation systems employing photovoltaic (PV) array and wind energy conversion system (WECS) operate in grid-tied mode, the power fluctuations affect the power quality of the grid. In a hybrid AC-DC microgrid (HMG), the dynamics of DC and AC subgrids influence each other. This paper proposes a supercapacitor based novel power smoothing methodology for the HMG with PV array, WECS, fuel cell (FC) and electrolyzer (EL) based hydrogen storage system considering the power fluctuations in both subgrids. The power smoothing technique on the DC subgrid aims to facilitate instantaneous power balance. The Kalman filter (KF) based velocity smoothing (KFV) approach is developed for the WECS. The KFV technique is compared with the power smoothing techniques presented in the literature. The KFV method is found to be effective in computing the smooth power reference for the supercapacitor system. By incorporating the proposed power smoothing technique in the HMG, the stress on the interlinking converter (ILC) and utility grid are minimized and the power quality is enhanced

A novel bio-inspired stochastic framework to solve energy management problem in hybrid AC-DC microgrids with uncertainty

This paper introduces an effective intelligent framework for the optimal energy management of hybrid AC-DC microgrids in the presence of varied renewable energy sources and storage units. In order ...

A novel bio-inspired stochastic framework to solve energy management problem in hybrid AC-DC microgrids with uncertainty

A novel bio-inspired stochastic framework to solve energy management problem in hybrid AC-DC microgrids with uncertainty

Research on Coordinated Control Strategy of AC-DC Hybrid Microgrid Bidirectional Converter

Based on the improved droop control of the bidirectional converter controlled by the DC (direct current) side power quantity, a coordinated control scheme with energy storage is proposed. Not only can the two-way converter automatically and smoothly switch in the rectification, inverter, and idle modes, but also the energy storage device can perform coordinated control in the DC side idle mode to maintain the DC bus voltage stability. Using DC side power control, there is no need to switch control strategies to meet islanding and grid-connected modes. The simulation results show that improved droop control can reduce frequent actions of power electronic devices caused by small-range fluctuations in DC bus voltage and AC (alternating current) frequency. Coordinated control can make the DC bus voltage more stable, ensure stable operation of the AC and DC hybrid microgrid, and improve system reliability.

An Active Damping Technique for PI and Predictive Controllers of an Interlinking Converter in an Islanded Hybrid Microgrid

This article highlights a voltage instability when the bidirectional interlinking converter (BIC) of a hybrid ac-dc microgrid operates as a constant power load (CPL). The instability is attributed to the impedance interactions seen at the dc port of the BIC. The BIC is operated with two different controllers, viz., a PI controller and a model predictive controller (MPC). In order to avert the instability, prohibiting impedance interactions is proposed as a design objective while determining the bandwidth of the PI controller. However, since a flexible control over bandwidth is not available with MPC, an active damping technique is proposed to address the instability. The proposed technique works equally well for the PI controllers with fixed or predetermined bandwidths. An important feature of the proposed technique is that it does not interfere with the original objectives of the controllers, once the instability is addressed. The technique comprises only one tuning factor, which does not depend on the BIC's internal parameters. As a result, it can easily be implemented as a general stabilizing scheme in any BIC. The efficacy of the proposed technique is verified through simulations, frequency-domain impedance analyses as well as experiments on a laboratory prototype of the BIC.

Regional integrated energy system dispatch strategy considering advanced adiabatic compressed air energy storage device

Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) has been considered to possess excellent potential of utilization in Regional Integrated Energy System (RIES) due to its various merits including superior ancillary service and multi-carrier energy generation and storage capacity. However, few studies have been reported on schedule strategies considering AA-CAES and its multiple applications in market environment. This paper presents a RIES schedule strategy considering multiple applications of AA-CAES accounting for trading strategy of Energy Hub Operator (EHO). The operation mechanism and the schedule framework of RIES are built at first. Then, key applications including heating service and reserve service of AA-CAES are analyzed and modeled, and the schedule model of RIES utilizing AA-CAES to optimize economy of EHO is developed. A RIES based on AC-DC hybrid micro-grid is used for case studies to assess the comprehensive benefits of AA-CAES for cogeneration, reserve providing and photovoltaic (PV) consumption. The results show that the multiple application capacity of AA-CAES lead to 21.89% increase in the overall profit of EHO. It improves the operation flexibility of RIES, optimizes market trading strategies of EHO and promotes the energy autonomy of RIES from various ways.

Unified Virtual Oscillator Control for Grid-Forming and Grid-Following Converters

A unified virtual oscillator controller (uVOC) is proposed, which enables a unified analysis, design, and implementation framework for both grid-forming (GFM) and grid-following (GFL) voltage-source converters (VSCs). Oscillator-based GFM controllers, such as dispatchable virtual oscillator control (dVOC), offer a rigorous analytical framework with enhanced synchronization but lack effective fault handling capability, which severely limits practical application. The proposed uVOC facilitates synchronization with an arbitrarily low grid voltage and fast overcurrent limiting; this enables effective fault ride-through unlike existing GFM controllers which typically switch to a back-up controller during the fault. GFM operation with uVOC is achieved in both grid-connected and islanded modes with seamless transitions between the two. In GFL converters, bidirectional power flow control and dc bus voltage regulation are achieved with uVOC. No phase-locked loop (PLL) is required for either GFL or GFM operation circumventing the synchronization issues associated with PLLs in weak grid applications. Detail small-signal models for GFM and GFL operation have been developed, and the systematic design guidelines for controller parameters are provided. The proposed controller is validated through hardware experiments in a hybrid ac-dc microgrid.